docs: def get_mute(self):
          """Return if the TV is muted."""
          params = '<InstanceID>0</InstanceID><Channel>Master</Channel>'
          res = self.soap_request(URL_CONTROL_DMR, URN_RENDERING_CONTROL,
                                  'GetMute', params)
          root = ET.fromstring(res)
          el_mute = root.find('.//CurrentMute')
          return el_mute.text != '0'